Environmental conditions significantly impact vehicle behavior. This is most commonly noted as degradation of vehicle stopping capabilities in inclement weather such as snow or ice. Such degradations mean that driver behavior should ideally adapt to match immediate road conditions, and that in some cases drivers should entirely avoid areas deemed to be too dangerous, for example those with “black ice”.
Road conditions can be generally estimated based on known weather conditions. However, both weather conditions and road temperatures can vary dramatically over short distances, so that general area weather forecasts are insufficient to provide specific driving advice to a vehicle in a particular area. Thus, more granular data on weather, and specifically on road conditions, would be of value to improve the safety of drivers.
Stopping distance and general vehicle safety also depends dramatically on the specific vehicle being driven. Vehicle stopping distances may vary based on vehicle model, vehicle weight, brake quality, and tire tread conditions. Thus, in a defined road location two vehicles with different characteristics may experience dramatically different stopping distances. As a result, knowledge of the weather or road conditions themselves are not sufficient to ensure driver safety.
The interplay between vehicle and road at a given instant is considered as an input in existing anti-lock braking systems (ABS). In such systems, the tangential acceleration of one or more wheels is measured and compared with the acceleration rate of the vehicle. Because the tire has lower mass than the vehicle it can decelerate much more quickly than the vehicle, and as a result the tire can “lock” in a state where it does not rotate. This locking is undesirable, because the co-efficient of friction of a tire in its locked state is substantially lower than the optimal coefficient of friction for that tire.
ABS uses a closed-loop control process to optimize the amount of rotation in the tire, and thus optimize coefficient of friction. In ABS, the amount of force applied to the brakes is automatically relaxed if lock (or, more generally, slip) is detected in order to allow the tire to rotate again. The braking is re-established once rotation is sensed. Ideally, this system functions so that the optimum coefficient of friction (corresponding to an optimum amount of tire slip) is maintained during braking.
While the above closed-loop system can provide excellent control over vehicle braking in an emergency situation, it is not capable of making predictions of future vehicle safety performance, or of assessing its performance versus a baseline. While ABS assures “optimum” braking for the particular emergency case, there is no ability to analyze whether this “optimum” is good enough—whether it represents a safety performance level that will be satisfactory in other situations.
Thus, while it is possible to provide general advice for a generic vehicle during inclement weather, and it is possible to optimize the safety of a specific vehicle after a loss of control has occurred, it is not currently possible to provide targeted advice to a vehicle about how well it can perform in specific weather conditions and/or upcoming road conditions.